There is increasing interest in allowing a wireless terminal to use different radio access technologies (RATs). There is a range of radio access technologies standardised by the 3rd-Generation Partnership Project (3GPP), including: Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and Global System for Mobile Communications (GSM). There is also a range of non-3GPP radio access technologies, such as wireless local-area network (WLAN) technology and Worldwide Interoperability for Microwave Access (WiMAX).
3GPP cellular networks offer coverage across a wide geographic area. The coverage area of 3GPP networks and non-3GPP networks may overlap. For example, Wi-Fi access points may be located within the coverage area of a 3GPP network. A non-3GPP technology may be integrated to some extent with a 3GPP network.
For a wireless operator, there is a challenge of providing intelligent mechanisms for interworking between different radio access technologies that have been standardised in isolation from each other.
A network-assisted interworking mechanism is described in 3GPP release 12. The 3GPP Radio Access Network (RAN) provides assistance parameters that help a terminal in performing access selection and traffic steering. The terminal is also provided with RAN rules/policies that make use of these assistance parameters. The assistance parameters may include threshold values for 3GPP signal related metrics, WLAN signal related metrics. One example of a RAN rule that uses the threshold value could be that the terminal should connect to a WLAN if the 3GPP signal level is below the signalled 3GPP signal level threshold at the same time as the WLAN signal level is above the signaled WLAN signal level threshold. The RAN may also indicate to the terminal which WLANs the mechanism should be applied to by sending WLAN identifiers.
The RAN assistance parameters (thresholds, WLAN identifiers) may be provided by the RAN by dedicated signaling and/or broadcast signaling. Dedicated parameters can only be sent to the terminal which has a valid Radio Resource Control (RRC) connection to the 3GPP RAN. A terminal which has received dedicated parameters applies dedicated parameters; otherwise the terminal applies the broadcast parameters. If no RRC connection is established between the terminal and the RAN, the terminal cannot receive dedicated parameters.
In some scenarios, the terminal may continue to apply the dedicated parameters which have been received from the RAN when the terminal leaves a connected mode. 3GPP Release 12 describes that a terminal leaving a connected mode (e.g. entering IDLE mode RRC_IDLE in LTE, URA_PCH, CELL_PCH in UMTS) will continue to apply dedicated RAN assistance parameters for a limited time duration. In LTE the suggested name of a timer for this time duration is called T350. In UMTS the suggested name is T330. After the timer has expired, the terminal will discard RAN assistance parameters and starts applying broadcast parameters.
A document “Technical Specification Group Radio Access Network; Study on Wireless Local Area Network (WLAN)—3GPP radio interworking (Release 12)”, 3GPP TR 37.834 3GPP, explored some possible ways of improving WLAN/3GPP interworking. Three possible solutions are described in this document. Solutions 1 and 2 describe that a terminal uses assistance parameters (broadcast or dedicated) to determine how to steer traffic, similar to 3GPP release 12 described above. Solution 3 describes that traffic steering of a terminal is controlled by the network using dedicated traffic steering commands. In a measurement control step, a terminal is configured with measurement procedures, including the identity of a target WLAN to be measured. The terminal is triggered to send a measurement report by rules set by the measurement control. The terminal then waits for a steering command message from the 3GPP network.
There is a need for an alternative method of interworking.